Steve Case, the AOL Time Warner chairman who orchestrated the biggest media merger ever, bringing Internet brands like America Online together with Time Warner’s movie studios, TV outlets, record labels, and publishing interests (including Entertainment Weekly and EW.com), announced this weekend that he’s stepping down from the company he helped build, effective at the time of the company’s annual shareholders’ meeting in May. He will continue, however, to serve on the board of directors.

Case, who built AOL from a start-up 18 years ago into a ubiquitous online brand, oversaw his company’s merger with Time Warner three years ago. Since then, however, the combined company has seen its stock price fall by 70 percent, despite the success of such properties as the ”Harry Potter” and ”Lord of the Rings” movie franchises, recording artists like Linkin Park and Faith Hill, and TV shows like ”Friends,” ”ER,” and ”The Sopranos.” (The Time Warner CEO who arranged the merger with AOL, Gerald Levin, stepped down a year ago.) In a message he sent on Monday to AOL Time Warner employees, Case wrote, ”This company does not need distractions at this critical time,” and noted that ”some shareholders continue to focus their disappointment with the company’s post-merger performance on me personally.”

AOL Time Warner CEO Richard Parsons also sent a message to employees on Monday, saying Case’s resignation was a decision he had ”reached entirely on his own.” Still, Parsons wrote, ”I look forward to continuing to work with Steve,” and said Case would continue to ”play an important role in making sure AOL Time Warner capitalizes on its tremendous promise.”